MoS2/Ti low-friction coating for gears

The applicability of a multilayer composite surface coating in gears is discussed in this work, mainly in what concerns to gear efficiency at normal operating conditions and to scuffing load capacity. The average friction coefficient between gear teeth is discussed and compared with uncoated steel gears.The disulfide molybdenum/titanium (MoS₂/Ti) composite coating is studied and the deposition procedure is described.Several screening tests, like Rockwell indentations, ball cratering, pin-on-disc and reciprocating wear, were performed to evaluate the adhesion to the substrate, the tribological performance of this coating and his applicability in heavy loaded rolling-sliding contacts, such as found in gears.FZG gear efficiency tests were performed using type C gears in order to evaluate the influence of the surface coating in gear efficiency, for a wide range of operating conditions. These tests in conjunction with a numerical model for the energetic balance of the FZG gearbox allowed the determination of the average friction coefficient between gear teeth, taking into account the presence of the surface coating.FZG gear scuffing tests were also performed using type C gears in order to evaluate the coating anti-scuffing performance, which proved to be very significant.     

Influence of low friction coatings on the scuffing load capacity and efficiency of gears

The influence of multilayer composite surface coatings on gear scuffing load carrying capacity, gear friction coefficient and gearbox efficiency is discussed in this work.The deposition procedures of molybdenum disulphide/titanium (MoS₂/Ti) and carbon/chromium (C/Cr) composite coatings are described.Tests reported in the literature, such as Rockwell indentations, ball cratering, pin-on-disc and reciprocating wear, confirm the excellent adhesion to the substrate and the tribological performance of these coatings, suggesting they can be applied with success in heavy loaded rolling–sliding contacts, such as those found in gears.FZG gear scuffing tests were performed in order to evaluate the coatings anti-scuffing performance, which both improved very significantly in comparison to uncoated gears. These results in conjunction with the friction power intensity (FPI) scuffing criterion allowed the determination of a friction coefficient factor X_SC to include the coating influence on the friction coefficient expression.The composite coatings were also applied to the gears of a transfer gearbox and its efficiency was measured and compared at different input speeds and torques with the uncoated carburized steel gears. Significant efficiency improvement was found with the MoS₂/Ti coating.     

螺旋锥齿轮数字化闭环制造的主要功能模块及其实现

基于中心计算机、国产齿轮测量中心和四轴联动数控铣齿机,将齿面的数控展成、数字化检测、计算机数值处理及数字化反调修正有机组合,构建了螺旋锥齿轮数字化闭环制造系统.实际应用表明,该系统能有效控制齿面几何精度与啮合质量,齿面质量稳定,加工效率高.     

Tribological investigation of low friction duplex surface treatment based on modified molybdenum disulphide coating

Abstract

One of the numerous possibilities to decrease friction and wear of sliding surfaces consists of the application of two-step (so called duplex) technologies. A novel duplex technology of gas sulphonitriding of a 41CrAlMo7 steel with subsequent deposition of a low friction MoS₂(Ti,W) coating by means of non-reactive magnetron deposition is described in the present paper. A pin and vee block geometry and a relevant Falex apparatus were chosen for implementation of a linear friction contact under heavy loadings. For comparison, five other treatments of machine parts applied in the industry were used in the paper as well. As a result of the tests, only the specimens after the proposed novel duplex treatment based on sulphonitriding and a low friction MoS₂(Ti,W) coating deposition outlasted the full load of 3500 N during 6 min without any failure from all the six different treatments investigated in the work.     

Surface finishing method for tooth flank of heat-treated surface-hardened small gears using a gear-shaped tool composed of alumina-fiber-reinforced plastic

High-accuracy gears are necessary to ensure the strength and silence of compact geared motors. Heat-treated surface-hardened small gears are employed in the reducer of a compact geared motor. The heat treatment causes distortion, which deteriorates the gear accuracy. To remove this distortion, surface-hardened small gears are rehobbed with a carbide hob. The rehobbing makes a tool mark on the gear tooth surface. This tool mark leads not only to strength deterioration of the tooth surface, but also vibration and noise. Therefore, a surface finishing method that eliminates the tool mark is required. However, it is difficult to finish surface-hardened small gears. This study proposes a tooth surface finishing method for a surface-hardened small gear. The method employs a gear-shaped tool composed of alumina-fiber-reinforced plastic (ALFRP) and a surface finishing device with an oscillation/traverse system. The proposed method was used in an experiment to remove the tool mark on the gear tooth flank of a surface-hardened small gear rehobbed by the carbide hob. The effectiveness of this method was verified. In addition, the processing mechanism of the ALFRP gearshaped tool was analyzed by observing the tool and the chips.     

Effect of surface coating and tin plating on friction characteristics of P-110 tubing for different thread compounds

Design factor problems related to galling failure have become an increasing concern for deepwater offshore wells. This paper presents the results of an experimental study conducted to determine friction characteristics of P-110 tubing coated with manganese phosphate and plated with tin. Six repeated tests were run to investigate the effect of lubrication type on friction characteristics of P-110 tubing by using thread compounds of API modified Threadkote-706, Shell Type-3 and Graphite/PTFE at a rotational speed of 5 rpm. In each test the bearing load was increased monotonically to a maximum value of 625 kN. The results of this study clearly indicate the importance of tin-plating in reducing the coefficient of friction.     

表面镍磷、镍钴合金镀层提高铸铁齿轮接触疲劳强度研究

研究了HT200灰铸铁齿轮轮齿表面Ni～P和Ni—Co合金镀层的工作性能,采用电子显微镜、光学显微镜等对合金镀层进行了表面形貌、纵剖面界面组织、合金镀层成分,显微硬度等的分析,接触疲劳的试验结果表明能显著提高接触疲劳寿命。     

A new fault diagnosis algorithm for helical gears rotating at low speed using an optical encoder

Helical gears are widely used in gearboxes due to its low noise and high load carrying capacity, but it is difficult to diagnose their early faults based on the signals produced by condition monitoring systems, particularly when the gears rotate at low speed. In this paper, a new concept of Root Mean Square (RMS) value calculation using angle domain signals within small angular ranges is proposed. With this concept, a new diagnosis algorithm based on the time pulses of an encoder is developed to overcome the difficulty of fault diagnosis for helical gears at low rotational speeds. In this proposed algorithm, both acceleration signals and encoder impulse signal are acquired at the same time. The sampling rate and data length in angular domain are determined based on the rotational speed and size of the gear. The vibration signals in angular domain are obtained by re-sampling the vibration signal of the gear in the time domain according to the encoder pulse signal. The fault features of the helical gear at low rotational speed are then obtained with reference to the RMS values in small angular ranges and the order tracking spectrum following the Angular Domain Synchronous Average processing (ADSA). The new algorithm is not only able to reduce the noise and improves the signal to noise ratio by the ADSA method, but also extracts the features of helical gear fault from the meshing position of the faulty gear teeth, hence overcoming the difficulty of fault diagnosis of helical gears rotating at low speed. The experimental results have shown that the new algorithm is more effective than traditional diagnosis methods. The paper concludes that the proposed helical gear fault diagnosis method based on time pulses of encoder algorithm provides a new means of helical gear fault detection and diagnosis.     

Synthesis of TiB2-reinforced iron-based composite coating

Titanium diboride (TiB₂) particulate reinforced Fe-based alloy composite coating was produced with ferrotitanium (FeTi), ferroboron (FeB), ferrotungsten (FeW), ferrochromium (FeCr), ferrovanadium (FeV) and ferromolybdenum (FeMo) powders by using gas tungsten arc welding (GTAW) process. The effects of GTAW processing on the microstructure of AISI-4340 alloy coating with ferro-alloy powders were investigated experimentally. Abrasive wear tests were performed on the coated surface of samples to examine the influence of vol% and the size of boride on wear rates. Depending on the results, it was seen that the samples coated by FeTi-FeW-FeB ferro-alloy powders mixture have the highest wear resistance.     

Investigation of FE model size definition for surface coating application

An efficient prediction mechanical performance of coating structures has been a constant concern since the dawn of surface engineering. However, predictive models presented by initial research are normally based on traditional solid mechanics, and thus cannot predict coating performance accurately. Also, the high computational costs that originate from the exclusive structure of surface coating systems (a big difference in the order of coating and substrate) are not well addressed by these models. To fill the needs for accurate prediction and low computational costs, a multi-axial continuum damage mechanics (CDM)-based constitutive model is introduced for the investigation of the load bearing capacity and fracture properties of coatings. Material parameters within the proposed constitutive model are determined for a typical coating (TiN) and substrate (Cu) system. An efficient numerical subroutine is developed to implement the determined constitutive model into the commercial FE solver, ABAQUS, through the user-defined subroutine, VUMAT. By changing the geometrical sizes of FE models, a series of computations are carried out to investigate (1) loading features, (2) stress distributions, and (3) failure features of the coating system. The results show that there is a critical displacement corresponding to each FE model size, and only if the applied normal loading displacement is smaller than the critical displacement, a reasonable prediction can be achieved. Finally, a 3D map of the critical displacement is generated to provide guidance for users to determine an FE model with suitable geometrical size for surface coating simulations. This paper presents an effective modelling approach for the prediction of mechanical performance of surface coatings.     

Amorphous diamond coating of tungsten carbide and titanium carbonitride for erosive slurry pump component service

Tungsten carbide spray coatings have become well established for resisting abrasion and erosion in pumps used in conventional oil production and in oil sands operations. To achieve additional benefits from the extreme wear resistance of tungsten carbide its use is being extended to solid forms for some critical components. Slightly harder titanium carbonitride-based cermets have much lower density and coefficient of thermal expansion and for these reasons are being considered as an alternative to tungsten carbide. PVD amorphous diamond coating also has potential to further increase the service life of selected pump parts fabricated from solid cermets. Micro-abrasion testing and single scratch and nano-indentation evaluation have been carried out on non-coated and PVD amorphous diamond coated WC-4.8% TaC–4.5% TiC/6% Co–1% Cr and TiCN-17% WC/8% Mo materials. Data obtained illustrate that the tungsten–carbide based product has superior wear properties to the titanium carbonitride material and that PVD amorphous diamond coating of both cermets enhanced wear resistance significantly and displayed potential for successful service application.     

Planetary motion cross bar friction test for application in machining process

This paper describes a new method to evaluate the friction coefficient at the tool-work interface in machining process where high stress and temperature are caused. In order to examine the feasibility of the proposed method, the present report introduces the method and the results obtained only at room temperature. Ti6Al4V, SUS304, AISI1045, FCD 700, FCD 450 and FC300 were used as work materials, while TiN coated carbide tool, TiAlN coated carbide tool and P15 were used as tool materials. The proposed method provided the friction coefficients of different coatings against different work materials, and demonstrated the variability of friction coefficient and the anisotropy of surface roughness.     

Large-scale friction and wear tests on a hybrid UHMWPE-pad/primer coating combination used as bearing element in an extremely high-loaded ball-joint

The surfaces of a heavily loaded ball-joint were initially covered with a sliding spray and suffer wear. A solution is found by incorporating UHMWPE pads (Ultra high molecular weight polyethylene) with a carbon fibre/epoxy reinforced ring as sliding material into the chairs of the structure, while the steel ball-side is covered with a Zn-phosphate primer coating, protecting against corrosion. The local static and dynamic behaviour of the hybrid UHMWPE pads in contact with steel or Zn-coated counterfaces has been large-scale tested on loading capacity, low friction and wear resistance. For protection of the sliding counterface against wear, a polymer lip covering the carbon ring has been experimentally designed to flow over the carbon ring under high contact pressures, assuming the retained polymer disc under hydrostatic conditions. As such, the soft coating resists extremely high contact pressures (150 MPa) with good adhesion to the steel ball. However the application method should be carefully selected, sprayed coatings are the most favourable for low initial static friction. Calculated bulk and flashtemperatures revealed that the UHMWPE melting temperature is not exceeded, although softening of the coating under high contact pressures may be favourable for a ‘self-repairing’ ability. Pre-sliding creep and intermediate wear paths as manifesting in the ball-joint were simulated, indicating that the maximum design coefficient of friction is not exceeded. Test results are compared to FEM-calculations to verify the practical applicability of the modified sliding system.     

Modification of fretting fatigue behavior of AL7075-T6 alloy by the application of titanium coating using IBED technique and shot peening

In this work, improvement in fretting fatigue life of AL7075-T6 has been investigated by titanium surface coating using ion-beam-enhanced deposition (IBED) technique and shot peening. From the experiments, the following conclusions were derived: (i) Shot peening increased the fretting fatigue life up to 350%. (ii) Titanium coating increased the fatigue life up to 100% with respect to virgin specimens for low working stresses, while it reduced the fatigue life at higher working stresses significantly. (iii) Titanium coating+shot peening increased the fatigue life up to 130% with respect to the virgin specimens for low working stresses, while it reduced the fatigue life at higher working stresses significantly. The highest and the lowest increase in coefficient of friction are obtained for virgin and shot-peened+titanium-coated specimens, respectively. IBED surface-modification technique is not successful in reducing fretting fatigue, except at low stresses.     

High temperature friction and wear characteristics of various coating materials for steam valve spindle application

Various coatings such as chromium carbide (deposited by plasma spraying and detonation gun techniques), chromium oxide, chromium oxide+titania+silica, NiCrAlY, and Al₂O₃+NiAl, all deposited by plasma spraying; stelliting, and surface nitriding have been applied on X20CrMo V121 steel. This steel is used for high temperature applications such as steam turbine valve spindle. Friction and wear behavior of the surface coated and treated materials have been studied at an elevated temperature of 550°C while rubbing against graphite-filled stellited steel. These studies have been carried out on SRV Optimol reciprocating tribometer. Test parameters for tribological studies have been selected with a view to simulate operating conditions encountered in operation. Additionally, the structure, porosity, hardness, bond strength, and thermal cycling behaviour of these surface coated/treated materials have been characterised. Based on these laboratory investigations, chromium carbide coating deposited by plasma spraying technique has been identified as the most suitable coating for steam turbine valve spindle application. Process parameters have been established for deposition of chromium carbide coating by plasma spraying technique on actual valve spindles. The field results obtained are found to be commensurate with the laboratory findings.     

Cr2N/CrN multilayer coatings for wood machining tools

The present paper describes results from a recent research project aimed at forming a wear resistant coating based on chromium on tools to wood machining. Cr₂N/CrN multilayer coatings deposited on HS6-5-2 steel substrates using cathodic arc evaporation were tested. These coatings were formed from 7 bilayers being ca. 340 nm thick and equally thick Cr₂N and CrN layers. For comparison, Cr₂N and CrN monolayer coatings were also prepared. Hardness measurements, indentation and scratch tests, friction and wear were performed to characterize the mechanical properties. The wear tracks and Rockwell indentations enable to assess wear mechanisms of the coatings. The results of the Cr₂N/CrN coatings investigated show high hardness: ca. about 22 GPa and a critical force being higher than 95 N and a low wear rate.The industrial tests of planer knives with Cr₂N/CrN multilayer coatings were carried out on a down-spindle milling machine to determine the durability of tools with wear resistant coatings for woodworking. These tools show increase of “life time” two times. Another positive feature of the use of such tools is the increase of the quality of wood surface machined when compared with uncoated tools.     

Characterization of surface grooves and scratches induced by friction of C/C composites at low and high temperatures

Friction experiments were conducted on C/C composites at low and high temperatures during braking with the use of a pin-on-disc tribometer. The surface grooves formed were investigated by an optical camera and a laser profilometer, while scratches were characterized by optical microscopy. Damages were correlated with tribological performances (friction and wear). It is shown that friction at low temperature leads to high friction coefficient and wear rate, and to surfaces strongly grooved and abraded. For friction experiments performed at high temperature, they lead to lower friction coefficient and wear, and the resulting surfaces are rather smooth and slightly grooved.     

Effects of anti-wear additives on friction and wear properties of Cr2O3 coating

The effects of some anti-wear additives on the friction and wear behaviour of plasma-sprayed Cr₂O₃ coating were investigated using a block-on-ring tester at ambient conditions. The results show that zinc dialkyldithiophosphate (ZDDP), tricesyl phosphate (TCP) and tributyl phosphate (TBP) significantly reduce the wear of Cr₂O₃ coating lubricated by paraffin oil. Additive concentrations as well as sliding time have great influence on the wear. The friction coefficient varies slightly with test conditions. The analysis by XPS of worn surfaces indicates that the wear resistance of these additives is due to the formation of tribochemical reaction films by reacting with Cr₂O₃ coatings.     

New tribometer designed for the characterisation of the friction properties at the tool/chip/workpiece interfaces in machining

This work deals with the development of a new tribometer designed for the characterisation of the frictional properties at the tool/chip/workpiece interfaces in cutting processes. Based on a plane–sphere contact configuration, the experimental set‐up enables a continuous regeneration of the pin–workmaterial contact. The average contact pressure can be selected up to 3 GPa under sliding velocities reaching 16 m/s. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coefficient is quantified in parallel to the heat flux transmitted to the pin. This new system has been applied to the characterisation of the frictional properties during the dry machining of a 27MnCr5 annealed steel with a carbide cutting tool. The influence of the sliding velocity and of an additional TiN layer deposited by PVD on the carbide pins has been investigated in dry conditions. It has been shown that the sliding velocity is the more influential parameter, followed by the coating. Copyright © 2007 John Wiley & Sons, Ltd.     

Regenerating titanium ventricular assist device surfaces after gold/palladium coating for scanning electron microscopy

Titanium is one of the most commonly used materials for implantable devices in humans. Scanning electron microscopy (SEM) serves as an important tool for imaging titanium surfaces and analyzing cells and other organic matter adhering to titanium implants. However, high‐vacuum SEM imaging of a nonconductive sample requires a conductive coating on the surface. A gold/palladium coating is commonly used and to date no method has been described to “clean” such gold/palladium covered surfaces for repeated experiments without etching the titanium itself. This constitutes a major problem with titanium‐based implantable devices which are very expensive and thus in short supply. Our objective was to devise a protocol to regenerate titaniumsurfaces after SEM analysis. In a series of experiments, titanium samples from implantable cardiac assist devices were coated with fibronectin, seeded with cells and then coated with gold/palladium for SEM analysis. X‐ray photoelectron spectroscopy spectra were obtained before and after five different cleaning protocols. Treatment with aqua regia (a 1:3 solution of concentrated nitric and hydrochloric acid), with or without ozonolysis, followed by sonication in soap solution and sonication in deionized water, allowed regenerating titanium surfaces to their original state. Atomic force microscopy confirmed that the established protocol did not alter the titanium microstructure. The protocol described herein is applicable to almost all titanium surfaces used in biomedical sciences and because of its short exposure time to aqua regia, will likely work for many titanium alloys as well. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.